Co-Ni-base alloy

ABSTRACT

A Co—Ni-base alloy, being characterized in that a composition of the alloy comprises at least Co, Ni, Cr, Mo, W and Fe, and percentages by weight of the composition are from 25% to 45% of Co, from 25% to 40% of Ni, from 18% to 26% of Cr, from 3% to 11% of Mo, from 0.5% to 9% of W, wherein a sum of Mo and W is from 4% to 13% by weight, and from 1.1% to 5% of Fe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Co—Ni-base alloy, and, moreparticularly to a Co—Ni -base alloy having a high elasticity and a highcorrosion resistance for use in a small-size precision device and thelike, a mainspring using the Co—Ni-base alloy, and a method forproducing the mainspring.

2. Description of the Related Art

To date, a Co-base alloy, a Co—Ni-base alloy which is more efficientthan the Co-base alloy or the like has been used as a high elasticmaterial for use in a small-size precision device (for example, refer topatent document 1).

Further, since a high output torque, durability and corrosion resistanceare required for a mainspring of a wrist-watch, the Co-base alloy or theCo—Ni-base alloy which is high in Young's modulus or material strength,excellent in corrosion resistance and has a favorable plasticworkability has been used as a material for the mainspring. The Young'smodulus of the Co-base alloy which has conventionally been used in themainspring of the wrist-watch in many occasions is in the range of fromabout 2.0×10⁵ MPa to about 2.1×10⁵ MPa. As a method for producing themainspring of the wrist-watch which is aimed for a higher output torquethan before, a method in which a Co—Ni-base alloy having a compositioncomprising, in terms of percentages by weight, from 30.9% to 37.2% ofCo, from 31.4% to 33.4% of Ni, from 19.5% to 20.5% of Cr, from 9.5% to10.5% of Mo, from 0.1% to 0.5% of Mn, from 0.3% to 0.7% of Ti, from 1.1%to 2.1% of Fe, from 0.8% to 1.2% of Nb, from 0.01% to 0.02% of mischmetal and inevitable impurities, and having a Young's modulus of from2.3×10⁵ MPa to 2.4×10⁵ MPa was prepared by vacuum melting and, then,subjected to the steps of casting, forging, hot-rolling,hot-wire-drawing, a solution treatment, cold-wire-drawing and annealingand, thereafter, subjected to a cold-wire-drawing at a final processingratio of from 30% to 90% in terms of a reduction ratio in across-section area to produce a wire which was, then, cold-rolled so asto have a finishing thickness of a spring and, thereafter, subjected toan age-hardening treatment at a treatment temperature of from 400° C. to620° C. for from 2 to 3 hours in a vacuum or non-oxidation atmospherehas been known (for example, refer to patent document 2).

Patent document 1: Japanese Patent No. 3190566 (Pages 2 and 3); and

Patent document 2: Japanese Patent No. 3041585 (Pages 2 and 3).

Along with a performance enhancement of a small-size precision deviceand a severer using condition thereof, a further performance enhancementhas been required for a high elastic material.

Along with a performance enhancement of a mechanical wrist-watch or adiversification of added mechanisms thereof, a higher output torque hasbeen required for a mainspring which is an energy source, and there is aproblem in that a conventional mainspring is insufficient. However, aspace within the mechanical wrist-watch is limited and, accordingly, itis not advantageous to increase thickness or width of the spring.

The output torque of the mainspring is represented by the followingformula:T=Ebt ³ πN/6L,wherein

T: output torque;

E: Young's modulus of material;

b: width of spring;

t: thickness of spring;

N: number of effective turns of spring; and

L: length of spring.

As seen from the formula, a material having a high Young's modulus isnecessary for obtaining a high output torque without increasing thethickness or width of the spring. Further, the mainspring of thewrist-watch is ordinarily small in size such that the thickness andwidth thereof are approximately 0.1 mm and 1 mm, respectively.Therefore, it is required that the material for use in the mainspring ofthe wrist-watch has not only a high Young's modulus, but also afavorable plastic workability property such that it can be machined intoa thin narrow hoop (strip-shaped material). For this account, a materialwhich has a high Young's modulus, a favorable plastic workability, amainspring having a high output torque using the material and a methodfor producing the mainspring are required. Simultaneously, durability ofthe mainspring and improvement of corrosion resistance thereof are alsorequired.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, an alloy in which a strengtheningelement is newly added to a Co—Ni-base alloy to define a compositionand, as a result, mechanical strength is remarkably enhanced isprovided. It has been found that, in the Co—Ni-base alloy, W alone or acombination of W and Nb was added as a strengthening element to a mainelements of Co, Ni, Cr, Mo and the like to newly define a compositionrange thereof and, as a result, material strength was remarkablyenhanced compared with an example of a conventional Co—Ni-base alloy.Further, it has been found that a mainspring having high performance canbe obtained by using the Co—Ni-base alloy according to the presentinvention, performing plastic working so as to have a high Young'smodulus in a rolling direction of such rolled material and, afterworking, performing an age-hardening treatment.

The Co—Ni-base alloy according to the invention has a superplasticproperty and is, simultaneously, imparted with a high mechanicalstrength, fatigue strength and an excellent corrosion resistance. Amainspring was produced by the aforementioned alloy which has acomposition comprising at least Co, Ni, Cr, Mo, W, and Fe andpercentages by weight of the composition are from 25% to 45% of Co, from25% to 40% of Ni, from 18% to 26% of Cr, from 3% to 11% of Mo, from 0.5%to 9% of W, wherein a sum of Mo and W is from 4% to 13% by weight, andfrom 1.1% to 5% of Fe, and also has fine deformation twins in a parentphase. More preferably, the composition of the aforementioned alloycomprises at least one type or more of elements among Nb, Mn, B, Zr andTi, and percentages by weight of the elements contained in theaforementioned alloy are as follows: 0≦Nb≦2%; 0≦Mn≦2%; 0≦B≦0.02%;0≦Zr≦0.2%; and 0 ≦Ti≦1%.

This alloy has a favorable plastic workability and a low stacking faultenergy and, accordingly, has a high work hardening ability. When thealloy is subjected to cold-plastic working, fine deformation twins aredensely formed in an FCC phase which is the parent phase and the likeand, through a subsequent work-hardening, an alloy strength is enhanced.The cold plastic working ratio is preferably 50% or more. Further, asuperplastic phenomenon is expressed by the presence of such finedeformation twins.

A method for producing a mainspring comprises the steps of: mixingelements such that a composition of an alloy comprises, in percentagesby weight, from 25% to 45% of Co, from 25% to 40% of Ni, from 18% to 26%of Cr, from 3% to 11% of Mo, from 0.5% to 9% of W, wherein a sum of Moand W is from 4% to 13% by weight, and from 1.1% to 5% of Fe and meltingthe alloy; subjecting the alloy to cold-wire-drawing; cold-rolling thealloy; forming the alloy; and subjecting the alloy to an age-hardeningtreatment.

Preferably, a processing ratio of the cold-wire-drawing is 10% or morein terms of a reduction ratio in a cross-section area. Further, theage-hardening treatment is preferably performed at a treatingtemperature of from 400° C. to 700° C. in a vacuum or non-oxidationatmosphere.

The Co—Ni-base alloy according to the present invention is enhanced in amaterial strength compared with the conventional Co—Ni-base alloy. Forthis account, it is effective to use the Co—Ni-base alloy according tothe invention for the spring or the like for the precision device whichrequires high load, high reliability and high corrosion resistance and,therefore, it has an advantage such that it can correspond to a trend ofdown-sizing and being free of maintenance thereof and the like. Byprocessing the Co—Ni-base alloy according to the invention, themainspring having a high output torque, an excellent durability andcorrosion resistance can be obtained. When the mainspring according tothe invention is used as a power source of the wrist-watch, since alarge driving torque can be obtained without enlarging thickness orwidth thereof, it is possible to increase a moment of inertial of abalance wheel, thereby being capable of decreasing a change of a rate tobe caused by a vibration or a shock. Further, diversification of addedmechanisms or an increase of duration period of time can be realized.Still further, even when it is repeatedly used, since characteristicsthereof are hardly deteriorated, the high output torque can bemaintained. It is tough and is hardly broken. Furthermore, even when itis left in a humid environment caused by, for example, a climate, ahuman perspiration or the like, it performs a high corrosion resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table showing compositions of the Co—Ni-base alloys ofConventional Examples and Examples.

FIG. 2 is a table showing values of tensile strength and elongation ofeach of test pieces.

FIG. 3 is a table showing a composition of Conventional Example d.

FIG. 4 is a table showing a composition of Conventional Example e.

FIG. 5 is a table showing output torque and the number of effectiveturns.

FIG. 6 is a graph showing a relation of an age-hardening treatmenttemperature and torque (T 0.5) of an alloy according to the presentinvention.

FIG. 7 is a table showing output torque and the number of effectiveturns.

FIG. 8 is a table showing output torque and the number of effectiveturns.

DETAILED DESCRIPTION OF THE INVENTION

A composition of the Co—Ni-base alloy according to the present inventioncomprises at least Co, Ni, Cr, Mo, W and Fe, and, in terms ofpercentages by weight, from 25% to 45% of Co, from 25% to 40% of Ni,from 18% to 26% of Cr, from 3% to 11% of Mo, from 0.5% to 9% of W,wherein a sum of Mo and W is from 4% to 13% by weight, and from 1.1% to5% of Fe, and, further, has fine deformation twins in a parent phase.Preferably, the composition of the alloy comprises on type or more ofelements among Nb, Mn, B, Zr and Ti, and percentages by weight of theelements contained in the alloy are as follows: 0≦Nb≦2; 0≦Mn≦2%;0≦B≦0.02%; 0≦Zr≦0.2%; and 0≦Ti≦1%.

A mainspring is produced from the Co—Ni-base alloy having theaforementioned composition.

Since the alloy which is a material of the mainspring according to theinvention has a favorable plastic workability and has a low stackingfault energy, it has a high work-hardening ability. When it is subjectedto cold-plastic working, fine deformation twins are densely formed in anFCC phase or the like and, accordingly, work-hardened, thereby enhancingthe alloy strength thereof. When the mainspring is produced by using analloy which is added with W alone or a combination of W and Nb as astrengthening element, the mainspring having a high torque can beobtained.

This alloy is strengthened by solid-solution Mo in the parent phasewhich is the FCC phase, and a stacking fault energy is decreased therebya high work-hardening ability appears by solid-solution Cr and, further,the parent phase is more strengthened by solid-solution W. Stillfurther, when it is subjected to cold plastic working, fine deformationtwins are densely formed in the parent phase and, also, solute atoms aresegregated in the stacking fault and, therefore, dislocation motions areblocked and, accordingly, work-hardened, thereby enhancing the alloystrength. When it is subjected to an age-hardening treatment in awork-hardened state, the solute atoms are segregated in the stackingfault to fix such dislocation. That is, the alloy strength is furtherenhanced by so-called strain age-hardening. Addition of Nb enhancesstrain age-hardening ability. By enhancing the strength in such a manneras described above, tensile strength, yield-strength and Young's modulusare enhanced and, therefore, when the mainspring is produced by usingthis alloy, the mainspring having a high output torque and an excellentdurability can be obtained.

This alloy is prepared by vacuum melting and, then, subjected to thesteps of casting, forging, hot-rolling, hot-wire-drawing, a solutiontreatment, cold-wire-drawing, and annealing and, thereafter, subjectedto cold-wire-drawing at a processing ratio of 10% or more in terms of areduction ratio in a cross-section area. Since this alloy has arelatively large deformation resistance, it is preferable to performwire-drawing by using a back-tensioning wire-drawing machine. A wireobtained by such performance is cold-rolled without being subjected toannealing until thickness thereof comes to a finishing thickness of thespring.

The reason why it is subjected to rolling after subjected towire-drawing is that Young's modulus in a rolling direction of thethus-rolled material becomes higher than that of the rolled materialwhich has been subjected to rolling without being subjected to thewire-drawing and, accordingly, an output torque of the mainspring can beenhanced. The reason why the processing ratio of the wire-drawing is setto be 10% or more is that 10% is a lower limit that an effect ofenhancing Young's modulus in the rolling direction of the rolledmaterial appears. Further, when the cold-plastic working is performed insuch manner as described above, fine deformation twins are denselyformed in the parent phase which is a texture of the rolled material andthe like and, accordingly, it is work-hardened, thereby enhancing thestrength. This rolled material is cut so as to have a widthcorresponding to a finishing width of the spring, subjected to edgepolishing to form a hoop having a rounded corner. Thus-formed hoop issubjected to the steps of sizing, forming, welding, an age-hardeningtreatment, and a surface treatment to produce the mainspring. Theage-hardening treatment is performed at a temperature of from 400° C. to700° C. for from one to 10 hours in a vacuum or non-oxidationatmosphere. By such performance, the mainspring is strain-age-hardenedto further enhance the strength. In a manner as described above, themainspring having a high output torque and excellent durability andtoughness can be obtained.

Next, a reason why the composition range is defined is described. Thereason why Co and Ni are defined to be in the ranges of from 25% to 45%and from 25% to 40%, respectively, is that these ranges are optimal onesfor forming a consistent FCC phase, obtaining a favorable plasticworkability and a high work-hardening ability. The reason why Cr isdefined to be in the range of from 18% to 26% is that 18% or more isdesirable to obtain an excellent corrosion resistance and a highwork-hardening ability, while, when Cr is over 26%, a σ phase isprecipitated to cause a risk for allowing the mainspring to becomebrittle.

Next, a reason why Mo and W are defined is described. Mo and W areelements which most contribute to solid-solution hardning of the FCCphase. In a composition in which Co, Ni, and Cr are contained in theaforementioned ranges, respectively, the ranges in which Mo is from 3%to 11% and W is from 0.5% to 9%, wherein a sum of Mo and W is 4% or moreby weight are appropriate ones for solid-solution strengthening of theFCC phase. However, when the sum of the percentages by weight of Mo andW is unduly large, the σ phase is precipitated to cause a risk ofallowing the mainspring to become brittle. For this account, it isoptimal for obtaining the mainspring having a high output torque and anexcellent toughness that Mo and W are in the aforementioned ranges,respectively, wherein the sum of the percentages by weight of Mo and Wis in the range of from 4% to 13% by weight

Next, a reason for defining 0≦Nb≦2% is described. This alloy may beadded with either W alone, or a combination of W and Nb. Nb not onlyenhances the strain age-hardening ability, but also combines with C toform a carbide which is precipitated in a crystal grain boundary tocontribute to suppressing crystal grains form becoming rough and largeor strengthening the grain boundary. In such manner as described above,Nb contributes to enhancing the characteristics of the alloy for themain spring. However, when Nb is over 2% by weight, a δ phase isgenerated to deteriorate the characteristics of the alloy for themainspring. For this account, by defining the percentages by weight ofNb as being in 0≦Nb≦2%, the δ phase is not precipitated and,accordingly, a favorable plastic work ability is maintained and strengthafter subjected to the age-hardening treatment is enhanced, therebyenhancing the output torque of the mainspring. Further, when acombination of W and Nb is added, as a result, an amount of W can besmaller than that in a case in which W is added alone and, therefore, agrowth of dendrite of a cast texture can be suppressed, therebyenhancing forging workability.

A reason why Fe is defined to be in the range of from 1.1% to 5% is thatthe range is an optimal one for solid-hardening the FCC phase withoutdeteriorating oxidation resistance. Mn is effective in cleaning thealloy as a deoxidant or a desulfurigation element, and is effective inenhancing work-hardening ability caused by decreasing a stacking faultenergy. However, when an amount thereof is unduly large, corrosionresistance become deteriorated. For this account, an optimal range of Mnis 0≦Mn≦2% by weight. B is effective in enhancing strength of thecrystal grain boundary to enhance workability; however, when an amountthereof is unduly large, workability is deteriorated to the contrary.For this account, an optimal range of B is 0≦B≦0.02% by weight. Zr iseffective in enhancing the strength of the crystal grain boundary at anelevated temperature to enhance hot-workability; however, when an amountof Zr is unduly large, workability is deteriorated to the contrary. Forthis account, an optimal range of Zr is 0≦Zr≦0.2% by weight. Ti has, asa deoxidant, effects in cleaning the alloy and suppressing the crystalgrain from becoming rough and large; however, when an amount of Ti isunduly large, a η phase is formed to hinder the workability. For thisaccount, an optimal range of Ti is 0≦Ti≦1% by weight.

Hereinafter, embodiments are described. In FIG. 1, compositions of theCo—Ni-base alloys of Conventional Examples and Examples according to theinvention are shown in terms of percentages by weight. These alloys weremelted in a vacuum melting furnace and, then, cast. Each of theresultant alloy ingots was forged, hot-rolled and, then, cold-rolled toproduce a rolled material having a thickness of 0.5 mm by means ofcold-rolling reduction ratios of 50% and 75%. Test pieces were preparedin accordance with JIS specifications by using the thus-produced rolledmaterial. The thus-prepared test pieces were each subjected to anage-hardening treatment for two hours at a temperature of from 200° C.to 1000° C. in a vacuum heat-treating furnace. The resultant test pieceswere each subjected to a tensile test. In FIG. 2, shown are values oftensile strength σ_(B) (MPa) and elongation ε (%) of each of test pieceswhich have been subjected only up to such cold-processing and thosewhich have further been subjected to the age-hardening treatment: 500°C.×2 hours.

As is seen from FIG. 2, in the Co—Ni-base alloys according to thepresent invention (Examples 1 to 7), the tensile strength after theage-hardening treatment of 5000° C.×2 hours shows higher values by fromabout 12% to 15% compared with those of the conventional Co—Ni-basealloys (Conventional Examples a to c) Namely, it is found that materialstrength has been enhanced as an effect of adding W into the alloycomposition.

Mainsprings of the wrist-watches were produced by using an example ofthe Co—Ni-base alloy (Conventional Example d) for use in theconventional mainspring, another example of the Co—Ni-base alloy(Conventional Example e) for use in the conventional mainspring, andexamples of alloys (Examples 1 to 7) each for use in the mainspringaccording to the present invention to compare spring characteristicsthereamong. In FIGS. 3 and 4, shown are compositions of these alloysemployed in Conventional Example d and Conventional Example e,respectively.

Each of the above-described alloys was prepared by using a vacuummelting furnace and, then, subjected to the steps of casting, forging,hot-rolling, hot-wire-drawing, a solution treatment, cold-wire-drawing,and annealing and, subsequently, subject to wire-drawing of 60% in termsof a reduction ratio in a cross-section area at room temperature byusing a back-tensioning wire-drawing machine, thereby producing a wirehaving a diameter of 3 mm. The thus-produced wire was rolled until ithad a finishing thickness of a mainspring and, then, cut widthwise so asto have a spring finishing width to produce a hoop having a thickness of0.12 mm and a width of 0.95 mm and, thereafter, an edge portion of thethus-produced hoop was subjected to polishing. Subsequently, theresultant hoop was cut to have a length of 370 mm and, then, aleading-end portion thereof was provided with a square hole and formedand, thereafter, a trailing-end thereof was welded with an outer hookingpart. Thereafter, the resultant hoop was subjected to the age-hardeningtreatment at each of 400° C., 500° C., 600° C., 650° C. and 700° C. for2 hours in a vacuum atmosphere and, lastly, a surface treatment wasperformed such that TEFLON was applied thereto. In such a manner asdescribed above, each of mainsprings was produced. The mainspring wasinserted in a barrel and, then, spring characteristics were examined. Aninner diameter of the barrel and a winding-core diameter were 10.60 mmand 2.80 mm, respectively.

In FIG. 5, in regard to Conventional Example d, Conventional Example eand Examples 1 to 7 according to the present invention which each havebeen subjected to an age-hardening treatment at −500° C., T 0.5 (outputtorque in a state in which a portion of the mainspring corresponding to0.5 hour was unwound after fully wound up), T 24 (output torque in astate in which a portion of the mainspring corresponding to 24 hours wasunwound), and the number of effective turns N of the spring which isrelated with a duration period are shown. In FIG. 6, shown is a graphillustrating a relation between an age-hardening treatment temperatureand T 0.5.

As is seen from FIG. 5, Examples according to the present invention eachhave a higher output torque by about 33% in T 0.5 and by about 38% in T24 than that of Conventional Example d and by about 15% in T 0.5 and byabout 17% in T 24 than that of Conventional Example e. In a case inwhich the output torques of Examples and Conventional Examples areallowed to be same with each other, since thickness of the spring ofExamples according to the present invention can be smaller than those ofConventional Example d and Conventional Example e, the number ofeffective turns N of the spring can be increased in a limited space and,accordingly, the duration period of time of the wrist-watch can beexpanded. Further, as is seen from FIG. 6, T 0.5 of each Exampleaccording to the invention can be enhanced by performing theage-hardening treatment in the temperature range of from 400° C. to 700°C., and T 0.5 becomes maximum in the range of from 500° C. to 600° C.

Next, a spring endurance test (acceleration test offully-wound-fully-unwound repetition) was conducted to examine an outputtorque and the number of turns and the number of repetitions whichreached a rapture after 500 repetitions. In FIG. 7, in regard toConventional Example d and Conventional Example e, Examples 1 and 2 asbeing representative of Examples according to the invention, the outputtorque and the number of turns after 500 repetitions in a case of beingsubjected to the age-hardening treatment at 500° C. for 2 hours areshown, while, in FIG. 8, the number of repetitions which reached arapture is shown. It is found that Examples according to the inventionare each small in torque deterioration or decrease in the number ofturns to be caused by fatigue of the spring generated by being subjectedto a 500-time repetition, and are each equivalent or higher in thenumber of repetitions which reached a rapture, and are, also, excellentin durability, compared with Conventional Example d and ConventionalExample e.

Further, Examples of the mainspring according to the invention havedescribed only about manually wound mainsprings; however, similarexcellent spring characteristics can be obtained also in automaticallywound mainsprings. Further, since the mainspring according to theinvention contains a large amount of elements such as Cr and the likewhich enhance the corrosion resistance and a small amount of Fe, it hasan extremely favorable corrosion resistance and, when it was subjectedto an immersion test in artificial human perspiration and a salt waterspray test, stain or discoloration was not generated.

It will be obvious to those having skill in the art that many changesmay be made in the above-described details of the preferred embodimentsof the present invention. The scope of the present invention, therefore,should be determined by the following claims.

1. A Co—Ni-base alloy, being characterized in that a composition of thealloy comprises at least Co, Ni, Cr, Mo, W and Fe, and percentages byweight of the composition are from 25% to 45% of Co, from 25% to 40% ofNi, from 18% to 26% of Cr, from 3% to 11% of Mo, from 0.5% to 9% of W,wherein a sum of Mo and W is from 4% to 13% by weight, and from 1.1% to5% of Fe.
 2. The Co—Ni-base alloy as set forth in claim 1, beingcharacterized in that the composition of the alloy comprises one type ormore of elements among Nb, Mn, B, Zr and Ti, and percentages by weightof the elements contained in the alloy are as follows: 0≦Nb≦2%,;0≦Mn≦2%; 0≦B≦0.02%; 0≦Zr≦0.2%; and 0≦Ti≦1%.
 3. The Co—Ni-base alloy asset forth in claim 1 or 2, being characterized by having been subjectedto cold-plastic working.
 4. The Co—Ni-base alloy as set forth in claim3, being characterized in that a processing ratio of the cold-plasticworking is 50% or more.
 5. The Co—Ni-base alloy as set forth in anyoneof claims 1, and 2, being characterized by having been subjected to anage-hardening treatment.
 6. The Co—Ni-base alloy as set forth in claim5, being characterized in that a temperature of the age-hardeningtreatment is from 200° C. to 700° C.
 7. The Co—Ni-base alloy as setforth in any one of claims 1 and 2 being characterized by having finedeformation twins in a parent phase.
 8. A mainspring, beingcharacterized by comprising the Co—Ni-base alloy as set forth in any oneof claims 1 and
 2. 9. A method for producing a mainspring comprising thesteps of: mixing elements such that a composition of an alloy comprises,in terms of percentages by weight, from 25% to 45% of Co, from 25% to40% of Ni, from 18% to 26% of Cr, from 3% to 11% of Mo, from 0.5% to 9%of W, wherein a sum of Mo and W is from 4% to 13% by weight, and from1.1% to 5% of Fe and melting the alloy; subjecting the alloy tocold-wire-drawing; cold-rolling the alloy; forming the alloy; andsubjecting the alloy to an age-hardening treatment.
 10. The method forproducing the mainspring as set forth in claim 9, being characterized inthat a processing ratio of the cold-wire-drawing is 10% or more in termsof a reduction ratio in a cross-section area.
 11. The method forproducing the mainspring as set forth in claim 9, being characterized byperforming the age-hardening treatment at a treating temperature of from400° C. to 700° C. in a vacuum or non-oxidation atmosphere.